1. Field of the Invention
The invention relates to new 3-hydroxy-2-cyclobuten-1-one salts as well as processes for their production and their use, especially for the production of squaric acid.
2. Background Art
Squaric acid is an interesting intermediate product for the production of pharmaceutical agents, dyes [Angew. Chem. 20, (1966), p. 931]and herbicides (Swiss Patent No. 609,837). Various processes for the production of squaric acid are known from the literature.
Several processes start from hexachloro-1,3-butadiene, which is cyclized to a chlorinated cyclobutene derivative with the help of sodium ethanolate. These intermediate products are hydrolyzed to squaric acid with sulfuric acid or other acids [Roedic, A., and Bernemann, P., Liebigs Ann. Chem., (1956), 600, p. 1; Maahs. G.. Liebigs Ann. Chem., (1965), 686, p. 55; Angew. Chemie, (1963), 75, p. 982; Uehara. A., and Tsuchiva. R.. Sci. Rep. Kanazawa Univ., (1980), 25, p. 83; Fan, R.. et al., Chemical Abstracts, (1987), 106, 103798c]. Instead of sodium ethanolate, morpholine is also used [Maahs. G. and Hegenberg. P., Angew. Chemie, (1966), 78, p. 927; Schmidt. A.H.. and Ried. W., Synthesis, (1978), p. 869; Gadek. T.R.. et al., (1976), U.S. Pat. No. 4,104,308; Paine. A.J., Tetrahedron Letters, (1984), 25, p. 135]. The cyclization can also take place purely thermally [Mueller, W.. (1976), German PS 2,618,557; Schroeder. M.. and Schaeoer. W., (1976), DE-PS 2,623,836; Maahs. G.. and Rombusch. D.. (1978), German PS 2,824,558; Rombusch. K.. and Maahs. G., (1983), German OS 3,314,431]. Drawbacks of all of these processes are either modest yields or high expenses (e.g., distillation with an extreme reflux ratio) and the special safety measures, which are necessary during handling of the carcinogenic feedstock hexachloro-1,3-butadiene.
According to another process [Bellus. D.. et al., Helv. Chim. Acta, 61, 1978), p. 1784], squaric acid in a 70 percent yield is obtained from the fungus metabolite moniliformin by bromination and hydrolysis. But moniliformin occurs in nature only in small amounts, and the known synthesis for it are expensive and produce only modest yields.
A further process, that is, the electrochemically reductive tetramerization of carbon monoxide to squaric acid, requires considerable equipment and yields a product mixture from which squaric acid is difficult to obtain in pure form. [Silvestri. G.. et al., Gazz. Chim. It., (1972), 102, p. 818; German OS 2,235,882; U.S. Pat. No. 4,461,681; U.S. Pat. No. 4,523,980; Fabre. P.L.. et al., Bull. Soc. Chim. Fr., (1988), p. 933].